a) Field of the Invention
The present invention relates generally to an assembly and method for preventing slippage between load carrying members that are clamped together. More specifically, the invention relates to a surface finish modification that enhances the frictional characteristics of a ring gear back face that engages the flange face of the differential case.
b) Description of the Prior Art
There are many assemblies where torque or shear loads are transferred between two members and the members are joined to each other in a clamped or bolted connection. Such assemblies may be dynamic as in drive trains, or static as in frame elements. It is highly desirable that these connections eliminate any relative slippage between the parts under imposed shear or torsion loads.
The prior art has used several methods to eliminate slippage in bolted clamp connections. These methods include providing an increased number of, or greater nominal diameter for the bolts between the connection such that friction will transfer torsion or shear loads, providing interlocking mechanical means to transfer loads between the two elements, or applying anaerobic adhesives to increase the shear capacity of the joint and eliminate slippage. Adding additional bolts to the connections increases the cost and assembly time to make the connection. The mechanical interlocking means used in such assemblies includes large diameter dowels, matched assemblies and lapped joints. However, the use of interlocking means decreases the interchangeability of parts and again increases the expense of the connection. In addition, a certain amount of clearance is still associated with dowels and matched assemblies. This clearance allows free motion across the joint prior to engagement of the interlocking components. Anaerobic adhesives represent a relatively new approach to the problem of connection slippage, but suffer the drawbacks of low torsional resistance, reduced effectiveness at elevated temperatures, and high sensitivity to assembly cleanliness.
It is also known to connect two members by deforming a third compliant element disposed between the two members so that the deformed element will engage the two members and transfer loads therebetween. However, these prior art devices involve initial large-scale deformation of the compliant element across regularly machined surfaces. Accordingly, these methods are expensive to employ and suffer the cost disadvantage associated with the interlocking joints previously described.
The prior art also describes a ring gear assembly comprising a gasket or coupling member between a ring gear and differential case. However, this assembly suffers from an inherent drawback due to the high compressibility of the aluminum gasket and other materials utilized as the coupling gasket.
This invention differs from the prior art in several ways. No intermediate material is introduced into the scheme of the fastened joint. Inherent piece part prices and assembly costs are lowered. More explicitly, the use of a deformable intermediate member is not desired. Ring gear screws are short in length by design. Ring gear screws are quite rigid with little elastic elongation, or stretch, when tightened. Due to this rigidity, an extremely hard, unyielding interface between the ring gear back face and differential case flange is desired. Slight yielding of an intermediate material quickly reduces the effective total fastened length. This reduction in length greatly reduces total clamp load and similarly the installation torque of the ring gear screw. This invention will maintain a hard, fastened joint with little chance of yielding, or material creep.
The need exists for an enhanced frictional connection between a ring gear back face and the flange face of the cast iron differential case to overcome the drawbacks inherent in the prior art.